Supporting material for medical purposes

ABSTRACT

The invention relates to the use of a non-woven fabric which is over-stitched by means of stitching threads as a supporting material for medical purposes. The invention is characterized in that the maximum tensile force of supporting material is equal to at least 30 N/cm and at least one side of the supporting material is partially or completely coated with a self-adhesive mass.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a backing material for medical purposes,preferably for orthopaedic dressings and bandages, which is coated on atleast one side completely or partially with a selfadhesive composition.

2. The Related Art

As backing materials for medical purposes, numerous materials based onfilms, wovens, knits, nonwovens, gels or foams have already beendisclosed and are also. employed in practice. The materials, which areoften coated with a self-adhesive composition as well, are required tobe skin-compatible, generally permeable to air and water vapour, andalso easy to model and conformable. Based on these requirements, a verythin or soft backing is frequently preferred. For handling and in use,however, the backing materials are also required to be of sufficientstrength and possibly of limited extensibility. Furthermore, the backingmaterial should retain sufficient strength and low extensibility evenafter becoming wet through.

Thin backings, especially those made of nonwovens, are highly permeableto air and water vapour. For certain applications, however, theirstrength is too low and their elongation too high.

Specific applications, an example being tapes for functional tapedressings for the prophylaxis and therapy of injuries, disorders andaltered states of the musculoskeletal system, require inelastic backingshaving high strength in the direction of stress. This is achieved byusing woven-fabric backings, usually of cotton or viscose. Backingmaterials of this kind, with appropriately high basis weight, aregenerally cost-intensive. High conformability and modelability can onlybe achieved by means of a woven fabric of relatively low strength. Whensuch a fabric is stressed, however, it generally exhibits a degree ofelongation, which is undesirable for its use.

When the dressings listed become wet through, they generally losestrength or become more extensible. This is likewise undesirable fortheir use and has to date been compensated by more frequent changing ofdressings, which, however, is cost-intensive.

Lamination with reinforcement threads has also been disclosed in theprior art by German Patent 571 244, although the reinforcement threadsemployed therein are not of high tenacity. The document, then, generallygives no indication of an inelastic backing.

In addition, AU 73555/74 describes by way of example a glassfilament-reinforced backing material for medical application based onfoam.

U.S. Pat. No. 4,668,563 describes a glass fibre-reinforced materialwhich, however, is elastic. All backing materials mentioned, however,are not reinforced by stitching.

DE 44 42 092 and DE U 94 01 037 describe adhesive tapes based onstitchbonded webs which are partially coated on the reverse side of thebacking. Such adhesive tapes are used preferably in cable bandaging.

DE 44 42 093 is also based on the use of a nonwoven as backing for anadhesive tape; in this case, a cross-laid fibre web is described whichis reinforced by the formation of loops from the fibres of the web. DE44 42 507 likewise discloses an adhesive tape for cable bandaging, butbases it on so-called Kunit or Multikunit webs.

A utility or special suitability of these backing materials for medicalpurposes, however, cannot be inferred from the documents cited. Inparticular, the publications give indications neither of sufficient skincompatibility of the adhesive compositions nor of functionally securedbonding on the skin or an advantageous permeability to air and watervapour.

U.S. Pat. No. 4,773,238 describes a fibre web with lengthwiseoverstitching, the stitching seams being intended to amount to no morethan 20% by weight based on the weight of the total nonwoven. Proposedin accordance with the invention is the utility as an insert for filtersin dust filtration.

U.S. Pat. No. 4,967,740 gives a general disclosure of backing materialsfor use in medical supply, which are produced in a one-step process. Inthis process, the backing is impregnated simultaneously with anelastomer and with a release solution. In this way, the material can bepresented without release paper on a roll.

In a listing of a large number of appropriate backings, mention is made,inter alia, of overstitched nonwovens, without the skilled worker beinggiven any indication as to how the nonwoven should, specifically, beconfigured in order to meet the requirements placed on a medicalbacking.

Highly adhesive orthopaedic bandages and other medical products areusually coated over the whole of their area with a rubber adhesivecomposition. These adhesive compositions then permit a high bondstrength on the reverse face of the backing, which ensures a stablefunctional dressing in the case of systems of circularly applieddressings with a plurality of plies.

The object of the invention was to provide a nonwoven-based backingmaterial which is suitable for medical requirements and does not havethe disadvantages known from the prior art. These inventions and otherobjects of the invention are achieved by the invention described herein.

SUMMARY OF THE INVENTION

Accordingly, a nonwoven overstitched by means of yarns is used asbacking material for medical purposes, the number of stitches on thenonwoven being advantageously at least 5/cm, preferably from 7/cm to50/cm. The ultimate tensile stress strength of the backing material isat least 30 N/cm, preferably from 40 to 450 N/cm, with particularpreference from 50 to 250 N/cm, and the backing material is coatedpartially or over its full area on at least one side with aself-adhesive composition.

The yarns preferably have a water absorption of less than 30%, withparticular preference less than 20%. The water absorption can beregenerated by the atmospheric humidity.

DETAILED DESCRIPTION OF THE INVENTION

Accordingly, materials which can be used for the yarns are,advantageously, polymeric fibres made from polypropylene, polyester,polyamide, aramid or polyethylene, and also mineral fibres such as glassfibres or carbon fibres. In addition it is also possible to usemultistrand yarns or mixed multistrands, especially Sirospun yarns. Forspecific applications, single- or multi-strand fibre blend yarns mayalso be employed. Furthermore, the yarns can have been at least partlycoloured in order to make the backing material more visually appealing.

For specific applications, the yarn can also be elastic. From this thereis then regenerated an elastic base support having an elongation of upto 250% at a load of 10 N/cm. Mention may be made here, for example, asa polyamide yarn (Lycra®, DuPont) [sic]. A backing material of this kindgenerates a compression force of from 0.2 N/cm to 10 N/cm at anelongation of from 20% to 70% and is used in compression technology.

In the case of the alternative embodiment of the subject-matter of theinvention, a nonwoven is used as backing material for medical purposes.In this case, the nonwoven is reinforced by the formation of stitchesformed by loops from the fibres of the web, the number of stitches onthe web being advantageously at least 5/cm, preferably from 7/cm to50/cm. The ultimate tensile stress strength of the backing material isat least 30 N/cm, preferably from 40 to 450 N/cm, with particularpreference from 50 to 250 N/cm, and the backing material is coatedpartially or over its full area on at least one side with aself-adhesive composition.

The backing materials are based on known nonwovens which aremechanically consolidated either by overstitching with separate yarns orby looping. In the first case, the resulting structures are the web-yarnstitchbonds. For their production, a fibre web is taken, which can, forexample, be in cross-plating configuration, and is overstitched withseparate yarns in pillarstitch formation or tricot formation.

These nonwovens are known by the name “Maliwatt” (from the companyMalimo) or Arachne.

With the second type of consolidation, again, preferably a cross-platedweb is taken. In the course of the consolidation operation, needles drawout fibres from the web itself and form them into loops, with stitchesbeing formed in pillarstitch formation. This web stitchbond is incirculation under the name “Malivlies” [Mali Fleece], again from thecompany Malimo.

An overview of the various kinds of mechanically consolidated fibrenonwovens can be found in the article “Kaschierung vonAutopolsterstoffen mit Faservliesen” [Laminating car upholsterymaterials with fibre webs] by G. Schmidt, Melliand Textilberichte6/1992, pages 479 to 486.

Advantageously, the webs have longitudinal stitches, in which case theorientation of the yarns ought to be aligned in accordance with thestresses on the backing material in use.

Starting materials which can be used for the nonwoven material aregenerally all organic and inorganic, natural- and synthetic-based fibrematerials. Examples that may be mentioned include viscose, cotton, silk,polypropylene, polyester, polyamide, aramid or polyethylene, and alsomineral fibres such as glass fibres or carbon fibres. The presentinvention is, however, not restricted to the said materials; rather, itis possible to use a large number of other fibres for web formation.

The fibres used to form the web preferably have a water retentioncapacity of more than 0.5%, preferably between 2 to [sic] 70%, withparticular preference between 3 and 50%.

In one preferred embodiment, the backing material has an ultimatetensile stress elongation of less than 40%, preferably less than 15%,with particular preference less than 10%.

For a web overstitched with yarns, this is achieved firstly by the useof a yarn material having a higher modulus of elasticity and secondlywith the use of stitching which ensures a yarn position which isstretched as much as possible.

Advantageous combinations of material are, for example, yarns ofhigh-strength polymer fibres such as polyamide, polyester, highlystretched polyethylene, or mineral fibres such as glass, and initial webmaterials such as cotton or staple viscose rayon.

For a web in which the formation of stitches takes place by the loopsbeing formed from the fibres of the web, the material of the initial webshould be selected accordingly; corresponding comments apply to thestitching.

It has also been found advantageous for the backing material to have abasis weight of less than 350 g/m², preferably from 10 to 180 g/m².

In one further advantageous embodiment, the backing material can be tornby hand perpendicular to the orientation of the stitches and/or in thedirection of the stitches.

Furthermore, the backing material may have been reinforced with one ormore monofil, multifil, staple fibre or spun fibre yarns and/or withoriented high-strength fibres, the yarns and/or fibres having inparticular a strength of at least 40 cN/tex. In addition it is alsopossible to employ multi-strand yarns or mixed multistrands, especiallySirospun yarns. For specific applications, single- or multi-strand fibreblend yarns may also be employed. These may comprise, for example,core-spun yarns or special staple fibre core-spun yarns. An advantagehere is that by combining different fibre types it is possible toachieve particular properties or specific properties in thereinforcement thread. Examples of this are the combinations of polyesteror polyamide with cotton or staple viscose rayon.

The reinforcement fibres or filaments here can consist of organic orinorganic materials: for example, and preferably, glass, carbon,polyester or specific polyamides, and the reinforcement fibres may alsohave been at least partly coloured in order to render the backingmaterial more visually appealing. In this way it is readily possible todifferentiate visually the reinforced backing. Coloured glass or polymerfilaments are particularly suitable for this purpose.

In one advantageous embodiment the backing material attains through theaddition of high-strength fibres or filaments an ultimate tensile stressstrength of more than 60 cN/tex, an ultimate tensile stress strength ofmore than 50 N/cm and an ultimate tensile stress elongation of less than25% with a basis weight of less than 140 g/m². A backing material ofthis kind is particularly suitable for acting as the backing for a tapestrip.

The number of attached or introduced filaments or high-strength fibresdepends primarily on the particular intended use and on the desiredultimate tensile stress strength and ultimate tensile stress elongationof the backing material, on its inherent nature and on the respectivestrength of the fibres and filaments themselves, and can therefore bevaried within relatively wide limits.

Advantageous combinations of material are, for example, reinforcementfilaments or fibres of high-strength polymer fibres such as polyamide,polyester, highly stretched polyethylene, or mineral fibres such asglass, and initial web materials such as cotton or staple viscose rayon.

In addition, the reinforcements are preferably inserted specifically inaccordance with the direction of stress of the backing material, i.e. inthe longitudinal direction. If more appropriate, however, they can alsoextend only or additionally in the transverse or oblique direction or,for example, in curved, spiral or zigzag formation, or randomly.

In one further advantageous embodiment, the backing material can be tornby hand perpendicular to the orientation of the reinforcement and/or inthe direction of the reinforcement.

With greater strength of the nonwoven material and an increasingproportion of reinforcement fibres, the backing withstands greaterstress and loading. Even very highly reinforced backing materials areable to absorb or allow the passage of large amounts of moisture, andhence provide a pleasant sensation for the user, with the reinforcementsabsorbing little or no moisture and so undergoing no change in theirproperties.

In the case of known ready-made tape dressings the reinforcementfilaments or fibres are preferably arranged equally in accordance withthe direction of stress in the applied state. Since these dressings havealready been cut to size or punched out, tearability by hand is not arequirement here.

A backing of this kind which is suitable for tapes has, for example, anultimate tensile stress strength of 50 N/cm and an ultimate tensilestress elongation of less than 20% for a basis weight of 200 g/m² or 250g/m², respectively, using the self-adhesive composition.

For the coating, preference is given to a self-adhesive compositionwhich has a high bond strength. For orthopaedic applications,especially, the adhesive composition ought to have a high initial tack.

As adhesive compositions it is possible with advantage to useself-adhesive compositions based on natural and synthetic rubbers and onother synthetic polymers such as acrylates, methacrylates,polyurethanes, polyolefins, polyvinyl derivatives, polyesters orsilicones with corresponding additives such as tackifier resins,plasticizers, stabilizers and other auxiliaries where necessary.

Thermoplastic hot-melt adhesive compositions, in particular, haveadvantageous properties and are favoured for reasons concerned with theproduction process.

Their softening point should be higher than 50° C., since theapplication temperature in the case of the coating is generally at least90° C., preferably between 120° C. and 150° C., or between 180° C. and220° C. in the case of special adhesive compositions such as silicones.If desired, post crosslinking by means of high-energy radiation such asUV rays or electron beams may be applied.

Preferred hot-melted adhesive compositions based on block copolymers arenotable for their diverse possibilities for variation, since thecontrolled reduction in the glass transition temperature of theself-adhesive composition as a result of the selection of thetackifiers, plasticizers, polymer molecule size and moleculardistribution of the starting components ensures the required bonding tothe skin in a manner appropriate to their function, even at criticalpoints of the human locomotor system.

The high shear strength of the hot-melt adhesive composition is achievedthrough the high cohesiveness of the polymer. The good tack results fromthe range of tackifiers and plasticizers employed.

For especially strongly adhesive systems, the hot-melt adhesivecomposition is preferably based on block copolymers, especially A-B-,A-B-A block copolymers or mixtures thereof. The hard phase A isprincipally polystyrene or its derivatives and the soft phase B containsethylene, propylene, butylene, butadiene, isoprene or mixtures thereof,particular preference being given here to ethylene and butylene ormixtures thereof.

Polystyrene blocks, however, may also be present in the soft phase B inamounts of up to 20%. The overall proportion of styrene should, however,always be less than 35% by weight. Preferably, styrene proportions ofbetween 5% and 30% are preferred, since a relatively low proportion ofstyrene makes the adhesive composition more conformable.

The controlled blending of diblock and triblock copolymers isparticularly advantageous, preference being given to a proportion ofdiblock Copolymers of less than 80% by weight.

In one advantageous embodiment the hot-melt adhesive composition has thefollowing stated composition:

from 10% by weight to 90% by weight of block copolymers,

from 5% by weight to 80% by weight of tackifiers such as oils, waxes,resins and/or mixtures thereof, preferably mixtures of resins and oils,

less than 60% by weight of plasticizers,

less than 15% by weight of additives, and

less than 5% by weight of stabilizers.

The aliphatic or aromatic oils, waxes and resins used as tackifiers arepreferably hydrocarbon oils, waxes and resins, the consistency of theoils, such as paraffinic hydrocarbon oils, or of the waxes, such asparaffinic hydrocarbon waxes, accounting for their favourable effect onbonding to the skin. Plasticizers used are medium-chain or long-chainfatty acids and/or their esters. These additions serve to establish theadhesion properties and the stability. If desired, further stabilizersand other auxiliaries are employed. Filling the adhesive compositionwith mineral or organic fillers, fibres or hollow or solid microbeads ispossible.

The self-adhesive composition has a softening point of more than 70° C.,preferably from 80° C. to 140° C.

The hot-melt self-adhesive compositions are preferably formulated sothat at a frequency of 0.1 rad/s they have a dynamic-complex glasstransition temperature of less than 5° C., preferably from −3 °C. to−30° C., with very particular preference from −9° C. to −25° C.

Stringent requirements are placed in terms of the adhesion properties onmedical backing materials. For ideal use the hot-melt adhesivecomposition should possess a high tack. There should be functionallyappropriate bond strength to the skin and to the reverse of the backing.So that there is no slipping, the hot-melt adhesive composition is alsorequired to have a high shear strength. By the controlled reduction inthe glass transition temperature of the adhesive composition, which is aresult of the selection of the tackifiers, the plasticizers, the polymermolecule size and the molecular distribution of the starting components,the required, functionally appropriate bonding to the skin and to thereverse of the backing is achieved. The high shear strength of theadhesive composition which is employed here is obtained by virtue of thehigh cohesiveness of the block copolymer. The good tack is the result ofthe range of tackifiers and plasticizers employed.

Product properties such as tack, glass transition temperature and shearstability can be quantified readily using a dynamo-mechanical frequencymeasurement. In this case, use is made of a rheometer controlled byshearing stress. The results of this measurement method give informationof the physical properties of a substance by taking into account theviscoelastic component. In this instance, at a predeterminedtemperature, the self-adhesive composition is set in oscillation betweentwo plane-parallel plates at variable frequencies and with lowdeformation (linear viscoelastic region). Via a pickup control unit,with computer assistance, the quotient (Q=tan δ) between the lossmodulus (G″, viscous component) and the storage modulus (G′, elasticcomponent) is determined.

Q=tan δ=G″/G′

A high frequency is chosen for the subjective sensing of the tack, and alow frequency for the shear strength.

The glass transition temperature is the temperature at which amorphousor partially crystalline polymers undergo transition from the liquid orrubber-elastic state to the hard-elastic or glassy state, or vice versa(Rompp Chemie-Lexikon, 9th Ed., Volume 2, page 1587, Georg Thieme VerlagStuttgart—New York, 1990). It corresponds to the maximum of thetemperature function at a predetermined frequency. For medicalapplications in particular, a relatively low glass transition point isrequired.

T_(g) Tack low Conformability high frequency/ Designation frequency lowfrequency/RT RT Hot-melt −10 ± 2° C. tan δ 0.35 ± 0.05 tan δ = 1.70 ±0.10 adhesive composition A Hot-melt  −9 ± 2° C. tan δ = 0.22 ± 0.03 tanδ = 1.00 ± 0.03 adhesive composition B

Preference is given in accordance with the invention to self-adhesivecompositions for which the ratio of the viscous component to the elasticcomponent at a frequency of 100 rad/s and at 25° C. is greater than 0.7,or to self-adhesive compositions for which the ratio of the viscouscomponent to the elastic component at a frequency of 0.1 rad/s at 25° C.is less than 0.4, preferably from 0.35 to 0.02 and, with very particularpreference, between 0.3 and 0.1.

It is also advantageous, especially with use for medical products, ifthe adhesive composition is applied partially to the backing material,for example by means of halftone printing, screen printing, thermoflexprinting or intaglio printing, because backing materials which have beenadhesively treated in a continuous applied line may, under unfavourablecircumstances, on application, induce mechanical irritations of the skinand are generally impermeable to air and water vapour.

Preference is given to application in the form of polygeometric domesand, especially, domes where the ratio of diameter to height is lessthan 5:1. Printed application of other forms and patterns on the backingmaterial is also possible—for example, a printed image in the form ofalphanumeric character combinations or patterns such as matrices,stripes and zigzag lines. The adhesive composition can be distributeduniformly over the backing material; alternatively, it can be appliedwith a thickness or density which varies over the area, as isappropriate for the function of the product.

The principle of thermal screen printing consists in the use of arotating, heated, seamless, drum-shaped, perforated, cylindrical screenwhich is fed via a nozzle with the preferred hot-melt self-adhesivecomposition. A specially shaped nozzle lip (circular or square bar)presses the hot-melt adhesive composition, which is fed in via achannel, through the perforation of the screen wall and onto the backingweb that is conveyed past it. This web is guided by means of acounterpressure roller against the external jacket of the heated screendrum at a rate which corresponds to the peripheral speed of the rotatingscreen drum.

In this context, the formation of the small domes of adhesive takesplace by the following mechanism:

The pressure of the nozzle bar conveys the hot-melt adhesive compositionthrough the screen perforation onto the backing material. The size ofthe domes formed is determined by the diameter of the screenperforation. The screen is lifted from the backing in accordance withthe rate of transportation of the backing web (rotary speed of thescreen drum). As a consequence of the high adhesion of the adhesivecomposition and the internal cohesion of the hot-melt, the limitedsupply of hot-melt adhesive composition in the perforations is drawn insharp definition from the base of the dome that is already adhering tothe backing and is conveyed by the pressure of the bar onto the backing.After the end of this transportation, the more or less strongly curvedsurface of the dome forms over the pre-defined base area in dependenceon the rheology of the hot-melt adhesive composition. The height-to-baseratio of the dome depends on the ratio of the performation diameter tothe wall thickness of the screen drum and on the physical properties(flow behaviour, surface tension and contact angle on the backingmaterial) of the self-adhesive composition.

For the screen in thermal screen printing, the web-to-hole ratio can beless than 3:1, preferably less than or equal to 1:1, and in particularequal to 1:3.

The above-described mechanism of formation of the domes preferentiallyrequires backing materials that are absorbent or at least wettable byhot-melt adhesive compositions. Non-wetting backing surfaces must bepretreated by chemical or physical techniques. This can be effected byadditional measures such as corona discharge, for example, or by coatingwith substances which improve wetting.

Using the printing technique indicated it is possible to lay down thesize and shape of the domes in a defined manner. The bond strengthvalues which are relevant for use and which determine the quality of theproducts formed are within very narrow tolerances in the case of propercoating. The base diameter of the domes can be chosen from 10 to 5000μm, the height of the domes from 20 to about 2000 μm, preferably from 50to 1000 μm, the low-diameter range being intended for smooth backingsand the range of greater diameter and greater dome height being intendedfor rough or highly porous backing materials.

The positioning of the domes on the backing is laid down in a definedmanner by the geometry of the applicator unit, for example the gravureor screen geometry, which can be varied within wide limits. With the aidof the parameters indicated it is possible, by way of adjustablevariables, to establish with very great precision the desired profile ofproperties of the coating, harmonized with various backing materials andapplications.

The backing material is preferably coated at a rate of more than 2m/min, preferably from 20 to 200 m/min, the chosen coating temperaturebeing greater than the softening temperature.

The self-adhesive composition can be applied to the backing material ata weight per unit area of greater than 15 g/m², preferably between 90g/m² and 400 g/m², with very particular preference between 130 g/m² and300 g/m².

The percentage of the area that is coated with the self-adhesivecomposition should be at least 20% and can range up to approximately95%, for specific products preferably from 40% to 60% and from 70% to95%. This can be achieved, if appropriate, by multiple application, inwhich case it is also possible, if desired, to use self-adhesivecompositions having different properties.

The combination of the preferred hot-melt adhesive composition and thepreferred partial coating on the one hand ensures reliable bonding ofthe medical product to the skin and, on the other hand, allergic ormechanical skin irritations, at least which are visually perceptible,are ruled out, even in the case of use extending over a number of days.The epilation of corresponding body regions and the transfer ofcomposition to the skin are negligible owing to the high cohesiveness ofthe adhesive, since the adhesive does not attach to the skin and hair;rather, the anchorage of the adhesive composition to the backingmaterial, at up to 12 N/cm (sample width), is good for medicalapplications.

Because of the intended breakage points that have been formed in thecoating, layers of skin are no longer displaced with one another oragainst one another in the course of detachment. The non-displacement ofthese layers of skin and the relatively low level of epilation lead toan unprecedented degree of painlessness in such strongly adheringsystems. In addition, the individual biomechanical control of bondstrength, which exhibits a demonstrable reduction in the bond strengthof these plasters, assists detachability. The applied backing materialshows good proprioreceptive effects.

Depending on the backing material and its temperature sensitivity, thehot-melt adhesive composition can be applied directly or can be appliedfirst to an auxiliary support and then to the ultimate backing. Inaddition, subsequent calendering of the coated product and/orpretreatment of the backing, such as corona irradiation, may beadvantageous for better anchorage of the adhesive film.

In addition, treatment of the hot-melt adhesive composition with anelectron beam postcrosslinking, or a UV irradiation, may result in animprovement in the desired properties.

In a further advantageous embodiment, the self-adhesive compositions arefoamed before being applied to the backing material.

In this case the self-adhesive compositions are preferably foamed usinginert gases such as nitrogen, carbon dioxide, noble gases, hydrocarbonsor air, or mixtures thereof. In many cases, foaming additionally bythermal decomposition of gas-evolving substances, such as azo, carbonateand hydrazide compounds, has been found to be suitable.

The degree of foaming, i.e. the gas content, should be at least about 5%by volume and can range up to about 85% by volume. In practice, levelsof from 10% by volume to 75% by volume, preferably 50% by volume, havebeen found to be appropriate. Operating at relatively high temperaturesof approximately 100° C. and with a comparatively high internal pressureproduces very open-pored adhesive foam layers which are particularlypermeable to air and water vapour. The advantageous properties of thefoamed self-adhesive coatings, such as low consumption of adhesive, hightack and good conformity, even on uneven surfaces, owing to theelasticity and plasticity, and also the initial tack, can be utilized tobest effect, very particularly, in the field of medical products.

The use of breathable coatings in conjunction with elastic and likewisebreathable backing materials produces a level of wear comfort which isperceived subjectively by the user as being more pleasant.

A particularly suitable method of preparing the foamed self-adhesivecomposition operates by the foam mixing system. In this system, thethermoplastic self-adhesive composition is reactive with the intendedgases such as, for example, nitrogen, air or carbon dioxide in variousvolume proportions (from about 10% by volume to 80% by volume) in astator/rotor system under high pressure and at a temperature above thesoftening point (approximately 120° C.). Whereas the gas entry pressureis greater than 100 bar, the mixing pressures between gas andthermoplastic in the system are from 40 to 100 bar, preferably from 40to 70 bar. The pressure-sensitive adhesive foam produced in this way cansubsequently be passed through a line into the applicator unit. In theapplicator unit, commercially customary nozzles, extruder systems orchamber systems are used.

By virtue of the foaming of the self-adhesive composition and the openpores in the composition which form as a result, and given the use of aninherently porous backing, the products coated with the adhesivecomposition have good permeability to water vapour and air. The amountof adhesive compositions required is considerably reduced withoutadverse effect on the adhesion properties. The adhesive compositionshave a surprisingly good tack, since per gramme of composition there ismore volume and thus more adhesion surface for wetting of the substratethat is to be bonded, and the plasticity of the adhesive compositions isincreased by virtue of the foam structure. Anchoring to the backingmaterial is also improved by this means. Moreover, the foamed adhesivecoating, as already mentioned, gives the products a soft and conformingfeel.

Foaming also generally reduces the viscosity of the adhesivecompositions. This lowers the melt energy, and even thermally unstablebacking materials can be coated directly.

The backing material coated with the adhesive composition can have anair permeability of greater than 1 cm³/(cm^(2*)s) preferably greaterthan 15 cm³/(cm^(2*)s), with very particular preference greater than 70cm³/(cm^(2*)s), and also a water vapour permeability of greater than 500g/(m^(2*)24 h), preferably greater than 1000 g/(m^(2*)24 h), with veryparticular preference greater than 2000 g/(m^(2*)24 h).

Furthermore, the backing material can also be provided with otherfinishes or treatments. These include, for example, corona, flame orplasma pretreatments, in order to increase the anchoring of theself-adhesive composition to the base web. In addition, the calenderingof the backing material or of the web as yet untreated withpressure-sensitive self-adhesive composition, for the purpose of furtherconsolidation and/or improvement in the anchoring of thepressure-sensitive self-adhesive composition, is an advantageoustreatment.

In addition, on the side opposite to that coated with self-adhesivecomposition, the backing material can be finished with a water-repellentlayer or impregnation which prevents rapid soaking on contact with wateror perspiration. In addition to the known impregnations, this can alsobe done by the sewing-on of a sheet, advantageously a water vapourpermeable sheet, by means of yarns directly during the consolidation ofthe web. The backing material can, furthermore, be finished with arelease layer or impregnation and/or coating which reduces the bondstrength of the self-adhesive composition. In this case as well, inaddition to the known release materials, it is also possible to sew on asheet, advantageously a water vapour permeable sheet, directly duringthe consolidation of the web.

Another procedure which has been found to be advantageous is thelamination of the web backing with at least one additional layer offoams or sheets, since by this means a combination of properties ofparticular type is obtained. A foam has a substantially higher dampingquality than an unlaminated backing. Sheets can be used, for example,for sealing the surface.

Finally, following the coating operation, the backing material can belined with a backing material which repels adhesive, such as siliconizedpaper, or can be provided with a wound pad or with padding.

Furthermore, the backing material can be coated with metallic substancesby vapour deposition.

It is particularly advantageous for the backing material to besterilizable, preferably by means of γ (gamma) radiation. Particularlysuitable for subsequent sterilization, therefore, are hot-melt adhesivecompositions based on block copolymers which contain no double bonds.This applies in particular to styrene-butylene-ethylene-styrene blockcopolymers or styrene-butylene-styrene block copolymers. This procedureis not accompanied by any application-significant changes in theadhesive properties.

The backing material of the invention has a bond strength on the reverseside of the backing of at least 0.5 N/cm, in particular a bond strengthof between 2.5 N/cm and 5 N/cm. Greater bond strengths may be achievedon other substrates.

The outstanding properties of the self-adhesively treated backingmaterial according to the invention suggest its use for medicalproducts, especially plasters, medical fixings, wound covers and alsoorthopaedic or phlebological bandages and dressings.

Advantageously it has been found that a reinforced backing material withsuch an adhesive coating, on becoming wet through—as is unavoidable, forexample, in the course of water sports activities—has a stability whichis better than that of customary commercial backing material. Therelative increase in the ultimate tensile stress elongation ofself-adhesively treated backing materials according to the inventionafter becoming wet through is only half as great as in the case ofcustomary commercial self-adhesively treated backing materials.

By virtue of this the backing materials of the invention, which indeedare thus essentially inelastic, become useful for specific medicalpurposes, and it is also possible to employ backing materials whose usehitherto was impossible owing to lack of strength and/or excessiveelongation.

With preference it is possible to use backing materials based on wovens,knits, nonwovens or composite products, provided they otherwise meet therequirements of medical use.

EXAMPLE

The text below describes by way of example a preferred backing material,without thereby wishing to restrict the invention unnecessarily.

The backing material used was a viscose-based nonwoven. The nonwoven wasoverstitched with a polyester yarn, the yarn count being 22/cm samplewidth. The water absorption of the polyester yarn was 0.3%. The backingmaterial was calendered and impregnated. The resulting backing materialhad an ultimate tensile stress strength of about 50 N/cm and an ultimatetensile stress elongation of 28% in the lengthwise direction. The basisweight was 120 g/cm². Wetting the backing material completely was notpossible owing to the choice of reinforcement materials. The backingmaterial had an air permeability of 100 cm³/(cm^(2*)s) and a watervapour permeability of greater than 2500 g/(m²*24 h) and could be tornboth partly and right through by hand in both crosswise and lengthwisedirections. Overall, the backing material in the soaked-through statecould be extended less than comparable backings which consisted only ofcotton.

The hot-melt adhesive composition was applied to the backing by thermalscreen printing.

The hot-melt adhesive composition was composed as follows:

an A-B/A-B-A block copolymer, which consists of hard and soft segments,with a ratio of A-B-A to A-B of 2:1 and a styrene content in the polymerof 13 mol-%; its proportion in the adhesive composition is 40% by weight(Kraton G),

a paraffinic hydrocarbon wax with a proportion in the adhesivecomposition of 52% by weight,

hydrocarbon resins with a proportion of 7.5% by weight (Super Resin HC140),

an ageing inhibitor with a proportion of less than 0.5% by weight(Irganox).

The components employed were homogenized in a thermal mixer at 185° C.The glass transition by the abovementioned method was −9° C.

Direct coating took place at 50 m/min and at a temperature of 120° C.The backing material was partially coated with 120 g/m² using a 14 meshscreen with a thickness of 300 μm.

The bandage produced by this method exhibited reversible detachment fromthe skin and good permeability for air and water vapour. Owing to thehigh shear stability of the hot-melt pressure-sensitive adhesive,sufficiently [sic] stabilization and a good proprioreceptive effect werefound. No skin irritations were observed, and the epilation observedfollowing the removal of the bandage was negligible.

What is claimed is:
 1. A backing material for medical purposes,comprised of a nonwoven overstitched by yarns, wherein the ultimatetensile stress strength of the backing material is at least 30 N/cm andthe backing material is coated partially or over its full area on atleast one side with a self-adhesive composition.
 2. A backing materialfor medical purposes, comprised of a nonwoven web which is reinforced bythe formation of stitches formed by loops from the fibers of the web,the number of stitches on the web being at least 5/cm, and wherein theultimate tensile stress strength of the backing material is at least 30N/cm, and the backing material is coated partially or over its full areaon at least one side with a self-adhesive composition.
 3. Backingmaterial according to claim 1, wherein the number of stitches on the webis at least 5/cm.
 4. Backing material according to claim 1 or 2, whereinthe webs have longitudinal stitches.
 5. Backing material according toclaim 3 wherein the backing material generates a compression force offrom 0.2 N/cm to 10 N/cm at an elongation of from 20% to 70%.
 6. Backingmaterial according to claim 1 or 2, wherein the backing material has anelongation of less than 250% at a load of 10 N/cm.
 7. Backing materialaccording to claim 1 or 2, wherein the backing material has an ultimatetensile stress elongation of less than 40%.
 8. Backing materialaccording to claim 1 or 2, wherein the backing material has a basisweight of less than 350 g/m².
 9. Backing material according to claim 1or 2, wherein the backing material is tearable by hand perpendicular tothe orientation of the stitches in the direction of the stitches, orboth.
 10. Backing material according to claim 1 or 2, wherein the fibresused to form the web have a water retention capacity of more than 0.5%.11. Backing material according to claim 1 or 2, wherein the backingmaterial is reinforced with one or more monofil, multifil, staple fibreor spun fibre yarns; with oriented high-strength fibres, or acombination thereof the yarns, fibres or both having a strength of atleast 40 cN/tex.
 12. Backing material according to claim 11, wherein thebacking material can be torn by hand perpendicular to the orientation ofthe reinforcement in the direction of the reinforcement or both. 13.Backing material according to claim 1, wherein the self-adhesivecomposition has a dynamic-complex glass transition temperature at afrequency of 0.1 rad/s of less than 5° C.
 14. Backing material accordingto claim 1, wherein the yarns have a moisture absorption of less than30%.
 15. Backing material according to claim 1, wherein theself-adhesive composition is a hot-melt adhesive composition. 16.Backing material according to claim 15, wherein the hot-melt adhesivecomposition is based on A-B or A-B-A block copolymers, or mixturesthereof, where phase A is principally polystyrene or its derivatives andphase B is ethylene, propylene, butylene, butadiene, isoprene ormixtures thereof.
 17. Backing material according to claim 15, whereinthe hot-melt adhesive composition consists of from 10% by weight to 90%by weight of block copolymers, from 5% by weight to 80% by weight oftackifiers, less than 60% by weight of plasticizers, less than 15% byweight of additives, and less than 5% by weight of stabilizers. 18.Backing material according to claim 15, wherein the hot-melt adhesivecomposition is applied by halftone printing, thermal screen printing orintaglio printing.
 19. Backing material according to claim 15, whereinthe hot-melt adhesive composition is applied in the form ofpolygeometric domes to the backing material.
 20. Backing materialaccording to claim 15, wherein the hot-melt adhesive composition iscoated on the backing material with a weight per unit area of greaterthan 15 g/m².
 21. Backing material according to claim 15, wherein thehot-melt adhesive composition is foamed.
 22. Backing material accordingto claim 1, wherein the coated backing material has an air permeabilityof greater than 1 cm³/(cm^(2*)s), or a water vapour permeability ofgreater than 500 g/(m^(2*)24 h) or both.
 23. Backing material accordingto claim 1, wherein on the side opposite that coated with theself-adhesive composition, the backing material is finished with awater-repellent layer, impregnation, release layer or coating. 24.Backing material according to claim 1, wherein at least one additionallayer comprising sheets, foams or nonwovens is applied on the backingmaterial.
 25. Backing material according to claim 1, wherein the coatedbacking material is covered after application of the self-adhesivecomposition or is provided with a wound pad or with padding.
 26. Backingmaterial according to claim 1, wherein the backing material is coatedwith metallic substances by vapor deposition.
 27. Backing materialaccording to claim 1, wherein the coated backing material issterilizable by γ (gamma) radiation.
 28. An improved method fororthopedic or phlebological bandaging or dressing wherein theimprovement comprises providing a bandage having a backing materialhaving a nonwoven web overstitched by yarns, wherein the ultimatetensile stress strength of the backing material is at least 30 N/cm andthe backing material is coated partially or over its full area on atleast one side with a self-adhesive composition.
 29. The methodaccording to claim 28, wherein the yarns have a moisture absorption ofless than 30%.
 30. An improved method for orthopedic or phlebologicalbandaging or dressing wherein the improvement comprises providing abandage having a backing material having a nonwoven web which isreinforced by the formation of stitches formed by loops from the fibersof the web, the number of stitches on the web being at least 5/cm, andwherein the ultimate tensile stress strength of the backing material isat least 30 N/cm, and the backing material is coated partially or overits full area on at least one side with a self-adhesive composition. 31.The method according to claim 30, wherein the number of stitches on theweb is at least 5/cm.
 32. The method according to claim 3, wherein thebacking material generates a compression force of from 0.2 N/cm to 10N/cm at an elongation of from 20% to 70%.
 33. The method according toclaim 28 or 30, wherein the webs have longitudinal stitches.
 34. Themethod according to claim 28 or 30, wherein the backing material has anelongation of less than 250% at a load of 10 N/cm.
 35. The methodaccording to claim 28 or 30, wherein the backing material has anultimate tensile stress elongation of less than 40%.
 36. The methodaccording to claim 28 or 30, wherein the backing material has a basisweight of less than 350 g/m².
 37. The method according to claim 28 or30, wherein the backing material is tearable by hand perpendicular tothe orientation of the stitches, in the direction of the stitches, orboth.
 38. The method according to claim 28 or 30, wherein the fibresused to form the web have a water retention capacity of more than 0.5%.39. The method according to claim 28 or 30, wherein the backing materialis reinforced with one or more monofil, multifil, staple fibre or spunfibre yarns; with oriented high-strength fibres, or a combinationthereof the yarns, fibres or both having a strength of at least 40cN/tex.
 40. The method according to claim 39, wherein the backingmaterial can be torn by hand perpendicular to the orientation of thereinforcement, in the direction of the reinforcement or both.
 41. Themethod according to claim 28, wherein the self-adhesive composition hasa dynamic-complex glass transition temperature at a frequency of 0.1rad/s of less than 5° C.
 42. The method according to claim 28, whereinthe self-adhesive composition is a hot-melt adhesive composition. 43.The method according to claim 42, wherein the hot-melt adhesivecomposition is based on A-B or A-B-A block copolymers, or mixturesthereof, where phase A is principally polystyrene or its derivatives andphase B is ethylene, propylene, butylene, butadiene, isoprene ormixtures thereof.
 44. The method according to claim 42, wherein thehot-melt adhesive composition consists of from 10% by weight to 90% byweight of block copolymers, from 5% by weight to 80% by weight oftackifiers, less than 60% by weight of plasticizers, less than 15% byweight of additives, and less than 5% by weight of stabilizers.
 45. Themethod according to claim 42, wherein the hot-melt adhesive compositionis applied by halftone printing, thermal screen printing or intaglioprinting.
 46. The method according to claim 42, wherein the hot-meltadhesive composition is applied in the form of polygeometric domes tothe backing material.
 47. The method according to claim 42, wherein thehot-melt adhesive composition is coated on the backing material with aweight per unit area of greater than 15 g/m².
 48. The method accordingto claim 42, wherein the hot-melt adhesive composition is foamed. 49.The method according to claim 28, wherein the coated backing materialhas an air permeability of greater than 1 cm³/(cm^(2*)s), or a watervapour permeability of greater than 500 g/(m^(2*)24 h) or both.
 50. Themethod according to claim 28, wherein on the side opposite that coatedwith the self-adhesive composition, the backing material is finishedwith a water-repellent layer, impregnation, release layer or coating.51. The method according to claim 28, wherein at least one additionallayer comprising sheets, foams or nonwovens is applied on the backingmaterial.
 52. The method according to claim 28, wherein the coatedbacking material is covered after application of the self-adhesivecomposition or is provided with a wound pad or with padding.
 53. Themethod according to claim 28, wherein the backing material is coatedwith metallic substances by vapour deposition.
 54. The method accordingto claim 28, wherein the coated backing material is sterilizable by γ(gamma) radiation.